1. Field of the Invention
The present invention relates to a car navigation device, and more particularly, to a car navigation device which provides a user with a forward real video-based navigation service using a forward real video photographed by a camera installed forward along the travel direction of a vehicle and a position information obtained from a GPS receiver, and, thereby minimizing the user distraction or anxieties due to confused information.
2. Description of the Related Art
A global positioning system (GPS) is a position determination system using artificial satellites. A GPS receiver receives electromagnetic wave transmitted from a known satellite, and obtains the position of an observation point from measured data of a time required until the electromagnetic wave reaches the observation point. The GPS is composed of a space section, a terrestrial section and a user section.
Since the position determination of the GPS is based on the four-dimensional coordinates positioning system using three-dimensional coordinates of an observation point, i.e., (X, Y, Z) and a time (t), the GPS can be effectively used that determining the position and velocity of an object traveling at high speed, such as an aircraft, a ship or a vehicle. Also, the GPS is advantageous in that observation can be made at any given time, and data is obtained in several seconds. A NAVSTAR (NAVigation Satellite Timing And Ranging) satellite, which was developed originally for military use by the United States Government, has been used as a GPS satellite. Since 1988, three satellites with orbital time intervals of 0.5 sidereal day, i.e., approximately, 11 hours and 58 minutes, have been substantially uniformly placed around each of six circular orbits, each being 20,183 km high from the land, being inclined at an angle of 55° relative to the equator and being separated from each other by multiples of 60° longitude, thereby enabling positioning from at least four satellites at any place of the world.
As to the accuracy levels achievable by using the GPS system, there are two types of signals available from the GPS satellite: an L1 signal; and an L2 signal. The first type of signal, i.e., L1 signal, includes both a C/A (Clear Acquisition) code for low accuracy data, and a P (Precision or Protection) code for high-accuracy data. The second type of signal, i.e., L2 signal, is modulated by only the P code.
Specifically, the L1 signal using the C/A code is only open for public use, while use of the P code is limited to military purposes by the agreement among governments concerned. A large portion of the satellite track errors, causing a positioning error, referred to as selective availability (SA) was purposefully induced by the U.S. Department of Defense to limit GPS accuracy to citizen applications, to a level of about 100 m. However, the recent technological development and proliferation of the GPS applications has urged the U.S. government to promulgate abolition of the SA in May 2000, leading to a considerable reduction in positioning error rate.
A conventional car navigation device includes a GPS receiver that receives position information of a vehicle during travel from a satellite, a map data storage device that provides map information about an area where the vehicle travels, a central processor unit (CPU) that processes position information and map information, and a display that displays a destination point, current position, and so on, and route controller that enables a user to arrive at his/her destination point in an ensured manner. The car navigation device, which is mounted on a vehicle, displays the current position and route information on the basis of the user's input information for destination point.
In the conventional car navigation device, navigation functions encompass dead reckoning, map matching, and GPS. The dead reckoning obtains the trip trajectory and relative position of a vehicle using a bearing sensor and a distance sensor mounted on the vehicle. The map matching compares the trip trajectory obtained by dead reckoning with a road based on map data to determine a transit road, thereby obtaining a map position of the vehicle. Korean Laid-open Patent Publication No. 2001-0024811 discloses a car navigation system which can increase the level of navigation accuracy by matching the position of a vehicle obtained by map matching with the absolute position of the vehicle, e.g., latitude and longitude information of the vehicle, obtained by GPS.
As shown in FIG. 1, the conventional car navigation device displays the current position of a vehicle on a two-dimensional plane map presented by a graphic image around a user's intended route to provide the user with information for the travel direction. The conventional car navigation device, however, provides a user with only the information about the travel direction of the car, rather than a real environment of a road on which the car is driving, making it difficult for a driver to find a correct road when the driver is new to the area or when the road is confusingly disorderly made.
To address the above problem, as shown in FIG. 2, another conventional car navigation device has been proposed in which surrounding environment 202, 204 is presented in a three-dimensional manner to be conformable to a real environment to provide travel route guidance to a user in a more user-friendly manner.
However, the conventional car navigation device has several disadvantages that the amount of map data to be offered to the user has become excessively large, requiring an increased production cost, and updating data of real road environments is retarded. Also, since the graphic image displayed on a screen of a monitor is in units of prominent buildings or roadside landmarks, finely-tuned environment data cannot be provided to the driver, which may make the guidance rough.
Further, in the conventional car navigation device, even when a turn-by-turn (TBT) information 304 saying as “Go straight ahead to a viaduct” is displayed on a predetermined region of the screen of a graphic map 302 for displaying the trip route, as shown in FIG. 3, it is often the case that the viaduct cannot be accurately located.